INHIBITION OF NICOTINIC ACETYLCHOLINE-RECEPTOR CHANNELS IN BOVINE ADRENAL CHROMAFFIN CELLS BY Y-3-TYPE NEUROPEPTIDE-Y RECEPTORS VIA THE ADENYLATE-CYCLASE PROTEIN-KINASE-A SYSTEM

The effect of neuropeptide Y NPY(1-36) and related peptides on the v oltage-dependent currents and the nicotinic acetylcholine receptor (nA ChR) currents (I-ACh) of bovine adrenal chromaffin cells was investiga ted using the whole-cell patch clamp technique. Catecholamine release from single chromaffin cells was measured by means of fast cyclic volt ammetry. The potency order of these peptides in inhibiting I-ACh evoke d by nicotine was NPY(1-36), NPY (16-36)>peptide YY(PYY)>Leu(31), Pro (34) NPY. NPY (16-36) produced a similar degree of inhibition, irresp ective of whether nicotine or an equipotent concentration of acetylcho line was used to evoke I-ACh. NPY (16-36) failed to alter voltage-depe ndent inward or outward currents. Intracellular cAMP, and extracellula r dibutyryl-cAMP, produced a slowly developing increase in I-ACh. Intr acellular cAMP, extracellular 8-Br-cAMP or dibutyryl-cAMP, and an inhi bitor of cyclic nucleotide phosphodiesterases 3-isobutyl-1-methylxanth ine (IBMX), decreased the inhibitory effect of NPY(16-36) on I-ACh. Al though the intracellular application of the cAMP-dependent protein kin ase A inhibitor PKI(14-24)amide alone did not alter I-ACh, it potent iated the effect of NPY(16-36) in interaction experiments. While the N PY(16-36)-induced inhibition of I-ACh was reversed on washout of the p eptide, the slightly shorter C-terminal fragment NPY(18-36) caused a l ong-lasting depression of both I-ACh and catecholamine secretion evoke d by nicotine. This depression was smaller in the presence of extracel lular 8-Br-cAMP than in its absence. NPY (18-36) did not alter the sec retory activity induced by a high concentration of potassium. It appea rs that, by activating Y-3 receptors, NPY inhibits nAChR-current and t he resulting secretion of catecholamines from bovine chromaffin cells. This process may involve a G protein-mediated decrease in intracellul ar cAMP with a subsequent decrease in the degree of phosphorylation of the nAChR channel.